General-relativistic neutrino-radiation hydrodynamics of crust ejection in magnetar giant flares
Abstract
Magnetar giant flares are thought to eject ≳ 10−9 M⊙ of baryons, as inferred from the radio afterglow of the 2004 flare of SGR 1806-20. One proposed mechanism is a shock driven into the neutron-star crust by the hot, high-pressure layer that the flare creates above the surface. The unbound crust could undergo r-process nucleosynthesis and power a short-lived "nova brevis". We study this crust ejection with general-relativistic neutrino-radiation hydrodynamics simulations performed with AthenaK, using a tabulated nuclear equation of state and two-moment neutrino transport, for flare pressures corresponding to magnetic fields B = 1015-1016.5 G, and compute the nucleosynthesis of the ejecta with a nuclear reaction network. We find that such flares unbind 10−10 to 5×10−8 M⊙ of crust. The ejecta keep the electron fraction of the crust to within a few hundredths, and weak interactions affect it mainly in the most energetic flares. The fast, high-entropy ejecta freeze out mostly as α particles and free neutrons. In the stronger flares nuclei up to the third r-process peak do form, but those with A ≥ 90 make up at most ≈ 8×10−4 of the ejected mass, or ≈ 3.5×10−11 M⊙ per flare, and less than 10−5 for B ≤ 1015.5 G. A nova brevis from these ejecta would be powered mainly by the decay of free neutrons. Like earlier work, our models assume spherical symmetry, a flare that covers the whole star, and no magnetic field. A field tangential to the surface would hold the crust down and weaken the shock, and a flare confined to part of the surface should eject proportionally less mass. We therefore regard our ejecta masses as upper limits for a given flare pressure, and expect realistic magnetar flares to produce negligible amounts of r-process material.
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BibTeX
@misc{pitik2026generalrelativistic,
title = {{General-relativistic neutrino-radiation hydrodynamics of crust ejection in magnetar giant flares}},
author = {Tetyana Pitik and David Radice and Jacob Fields and Yi Qiu},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.07022},
eprint = {2611.07022},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.07022},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - General-relativistic neutrino-radiation hydrodynamics of crust ejection in magnetar giant flares
AU - Tetyana Pitik
AU - David Radice
AU - Jacob Fields
AU - Yi Qiu
PY - 2026
DA - 2026/11/04
PB - arXiv
DO - 10.48550/arxiv.2611.07022
UR - https://arxiv.org/abs/2611.07022
AB - Magnetar giant flares are thought to eject ≳ 10^−9 M_⊙ of baryons, as inferred from the radio afterglow of the 2004 flare of SGR 1806-20. One proposed mechanism is a shock driven into the neutron-star crust by the hot, high-pressure layer that the flare creates above the surface. The unbound crust could undergo r-process nucleosynthesis and power a short-lived "nova brevis". We study this crust ejection with general-relativistic neutrino-radiation hydrodynamics simulations performed with AthenaK, using a tabulated nuclear equation of state and two-moment neutrino transport, for flare pressures corresponding to magnetic fields B = 10^15-10^16.5 G, and compute the nucleosynthesis of the ejecta with a nuclear reaction network. We find that such flares unbind 10^−10 to 5×10^−8 M_⊙ of crust. The ejecta keep the electron fraction of the crust to within a few hundredths, and weak interactions affect it mainly in the most energetic flares. The fast, high-entropy ejecta freeze out mostly as α particles and free neutrons. In the stronger flares nuclei up to the third r-process peak do form, but those with A ≥ 90 make up at most ≈ 8×10^−4 of the ejected mass, or ≈ 3.5×10^−11 M_⊙ per flare, and less than 10^−5 for B ≤ 10^15.5 G. A nova brevis from these ejecta would be powered mainly by the decay of free neutrons. Like earlier work, our models assume spherical symmetry, a flare that covers the whole star, and no magnetic field. A field tangential to the surface would hold the crust down and weaken the shock, and a flare confined to part of the surface should eject proportionally less mass. We therefore regard our ejecta masses as upper limits for a given flare pressure, and expect realistic magnetar flares to produce negligible amounts of r-process material.
ER -